The invention relates to a method for operating an air-compressing fuel-injection internal combustion engine having an exhaust gas post-treatment system with a particle filter and a nitrogen oxide reduction catalytic converter, in which a plurality of internal combustion engine operating settings are possible, with respective predefined values for predefined internal combustion engine operating parameters.
German patent document DE 101 55 339 A1 discloses a method for operating an internal combustion engine in which the coolant is heated rapidly by a heating operating setting, so that sufficient heat is quickly available for heating the passenger compartment. The method comprises setting internal combustion engine operating parameters which for the most part degrade the thermodynamic efficiency and cause a comparatively high release of heat. However, aspects relating to the emission of pollutants and to the consumption of fuel are not taken into account.
German patent document DE 103 23 245 A1 also proposes an operating setting with poor thermodynamic efficiency in order to increase the exhaust gas temperature of an internal combustion engine. The associated proposed measures are aimed in particular at heating an oxidation catalytic converter arranged in the exhaust gas system in the internal combustion engine, so that said oxidation catalytic converter can better convert pollutants. In this context, aspects which relate to the consumption of fuel are also largely left unconsidered.
One object of the present invention is to provide a method for operating an air-compressing fuel-injection internal combustion engine which, on the one hand, permits low emission of pollutants, while at the same time permitting low fuel consumption.
This and other objects and advantages are achieved by the method according to the invention for operating an air-compressing fuel-injection internal combustion engine, which is aimed, in terms of the emission of pollutants, in particular at low emission of particles and low emission of nitrogen oxide. For this purpose, an exhaust gas post-treatment system having a particle filter and a nitrogen oxide reduction catalytic converter is provided for the internal combustion engine. In order to achieve, on the one hand, optimum operation of the exhaust gas post-treatment system and, on the other hand, low consumption of fuel, a plurality of internal combustion engine operating settings with respective predefined values for predefined internal combustion engine operating parameters are provided. When the internal combustion engine warms up, a heating operating setting is set, and in the warmed-up state, (i.e., after warming up has taken place), a basic operating setting is set. The heating operating setting ensures that catalytic exhaust gas cleaning components, (in particular the nitrogen oxide reduction catalytic converter) in the exhaust gas post-treatment system quickly reach their operating temperature.
In this context, the basic operating setting is made more favorable in terms of consumption compared to the heating operating setting. If a predefinable first temperature threshold value in the exhaust gas post-treatment system is exceeded, the system changes from the heating operating setting to the basic operating setting. The upward crossing of the first temperature threshold value preferably characterizes a ready-to-operate state of an exhaust gas catalytic converter (in particular, of the nitrogen oxide reduction catalytic converter). This procedure shortens the warming up phase which is critical in terms of the emission of pollutants, therefore keeping the total pollutants generated in the warming up phase low. On the other hand, it is ensured that the heating operating setting, which is unfavorable in terms of consumption, is maintained for no longer than necessary. As a result, the additional consumption caused by the heating operating setting is minimized.
According to the invention, in the warmed-up state, at least one further, in particular a third, operating setting with an exhaust gas recirculation rate which is reduced compared to the basic operating setting is provided in addition to the basic operating setting.
An operating setting of the internal combustion engine within the meaning of the invention is characterized by a set of internal combustion engine operating parameters which determine the profile of the combustion of fuel in a combustion chamber or chambers of the internal combustion engine. Such internal combustion engine operating parameters can be set largely and/or mainly independent of the load rotational speed state of the internal combustion engine.
The internal combustion engine operating parameters which are decisive in terms of the combustion profile relate to the supply of both air and gas, as well as the supply of fuel to the combustion chambers. In particular, the internal combustion engine operating parameters which are decisive for an operating setting comprise the degree of exhaust gas recirculation, the degree of cooling of the recirculated exhaust gas and/or of the charge air of a supercharging unit and its charge air pressure, and the control of air movements in the combustion chamber, particularly in terms of turbulence in the form of swirl. In addition, the number, start and duration of fuel injection processes as well as the fuel injection pressure which is set in the context are also included, as are control times and/or the stroke of valves which determine the gas exchange and the compression ratio. The components and actuators which are necessary for this purpose are, insofar as they are necessary, to be considered as parts of the internal combustion engine here.
As far as the exhaust gas post-treatment system is concerned, in principle any component which is suitable for removing constituents of exhaust gas in the form of particles can be used as the particle filter. For example, what are referred to as wall flow filters, sintered metal filters, depth filters or open filter systems can be used, and a catalytic coating is advantageous in this context. The nitrogen oxide reduction catalytic converter can be, in particular, what is referred to as an SCR catalytic converter based on vanadium pentoxide and/or a noble metal. However, it is also possible to use a nitrogen oxide storage catalytic converter and/or nonselective, or less selective, denox catalytic converters. The exhaust gas post-treatment system preferably comprises further catalytic cleaning units. An oxidation catalytic converter, preferably in a position close to the engine, is particularly preferred.
Warming up within the sense of the present method is understood to mean the operating phase after the internal combustion engine starts until a component temperature and/or operating resource temperature which characterizes warming up is reached. This is preferably a temperature threshold value in the exhaust gas post-treatment system.
In the third operating setting according to the invention, the relatively high exhaust gas recirculation rates of approximately 50% to 60% (which are preferably provided for the basic operating setting) are reduced by approximately 10% to 40%, so that in the third operating setting exhaust gas recirculation rates of approximately 10% to 45% are preferred.
The third operating setting can be configured here for further improving the consumption of fuel. For this purpose, in addition to the reduction in the exhaust gas recirculation rate to approximately 25%, preferably one or more further internal combustion engine operating parameters (such as, for example, the start of a fuel main injection and/or the fuel injection pressure) are correspondingly adapted. A start of the fuel main injection which is earlier compared to the basic operating setting is typically set. In particular, in a third operating setting which is configured to be optimum in terms of consumption it is advantageous if the injection pressure is raised by approximately 50 bar to 500 bar compared to the basic operating setting which is less favorable in terms of consumption. Possible worsening of the raw emissions from the engine which are associated with this change does not affect the total emissions (exhaust end pipe emissions) because the exhaust gas post-treatment system is then fully functionally capable.
However, the third operating setting can also be configured to heat the exhaust gases. With this configuration, in addition to reducing the exhaust gas recirculation rate (in this case, by approximately 10%), one or more further internal combustion engine operating parameters are preferably also adapted compared to the basic operating setting. In this refinement, cooling of exhaust gas cleaning components which has occurred or threatens to occur due, for example, to unfavorable travel states, can be avoided or eliminated by the third operating setting, so that their functional capability is not adversely affected. An exhaust gas recirculation rate of approximately 45% to 55%, and therefore an only slightly smaller exhaust gas recirculation rate than in the basic operating setting, is preferably set. In addition, it is advantageous for application of heat to the exhaust gas to add a late fuel post-injection with a start of injection at approximately 60° CAaTDC to 160° CAaTDC (degrees of crank angle after the top dead center), whereas preferably no post-injection is provided for the basic operating setting.
In one refinement of the invention, the internal combustion engine is operated with a compression ratio of less than 19:1, at least in one of the combustion methods which are set in the warmed-up state. The internal combustion engine is preferably operated with a compression ratio of less than 18:1 and particularly preferably of less than 17:1. The compression ratio may be variable in this context, but it is preferably permanently predefined owing to the geometries and is of the same size for all cylinders of the internal combustion engine. Due to the comparatively low compression ratio for an air-compressing internal combustion engine, it can be operated with particularly low raw emissions of nitrogen oxide. The nitrogen oxide reduction catalytic converter can therefore operate particularly effectively, so that correspondingly low nitrogen oxide emission values are made possible for the exhaust end pipe emissions. If appropriate, the nitrogen oxide reduction catalytic converter can also be made smaller and therefore more cost effective than in internal combustion engines which are operated with a relatively high compression ratio. A relatively small nitrogen oxide reduction catalytic converter also exhibits improved warming up behavior and is easily accommodated in the exhaust gas system. The nitrogen oxide reduction catalytic converter then preferably has a catalytic converter volume which is less than three times, particularly preferably less than twice, the cubic capacity of the internal combustion engine.
In a further refinement of the invention, the first temperature threshold value characterizes a start of the effectiveness of the nitrogen oxide reduction catalytic converter, and an additive for nitrogen oxide reduction is added to the internal combustion engine exhaust gas in the warmed-up state upstream of the nitrogen oxide reduction catalytic converter. A temperature is preferably sensed in the bed of the catalytic converter or at the inlet end of the nitrogen oxide reduction catalytic converter and compared with a respective, stored reference value which correlates with or corresponds to what is referred to as the light-off temperature of the nitrogen oxide reduction catalytic converter. In this context the stored reference value can be adapted continuously or from time to time in accordance with an aging state of the nitrogen oxide reduction catalytic converter. If the reference value is exceeded, the combustion method is changed over, an enable signal for the supply of the additive is set and, if appropriate, the supply is started immediately. The nitrogen oxide reduction catalytic converter is preferably embodied as an SCR catalytic converter and the additive is ammonia, urea or some other substance which is capable of releasing ammonia.
In a further refinement of the invention, when the heating operating setting is active and a predefinable second temperature threshold value is exceeded in the exhaust gas post-treatment system, a separate fuel post-injection is activated. The other internal combustion engine operating parameters of the heating operating setting preferably remain unchanged. This is therefore a variant of a heating operating setting with an additional fuel post-injection. The activated fuel post-injection is preferably configured as a late, fuel post-injection which does not also burn and has a start of injection of approximately 140° CAaTDC. Therefore with this refinement of the method, the internal combustion engine first operates without late post-injection immediately after it starts with the heating operating setting active. The late post-injection is activated only when the second temperature threshold value is exceeded.
It is advantageous here if, immediately after the internal combustion engine starts, an early, accumulated post-injection which also burns is carried out and is also maintained after the late post-injection is activated. When the late post-injection is activated, a certain degree of warming up has already taken place so that condensable components which have possibly entered the exhaust gas through the post-injection are prevented from becoming deposited and raised hydrocarbon exhaust end pipe emissions are avoided.
In a further refinement of the invention, the second temperature threshold value characterizes the start of the effectiveness of an oxidation catalytic converter connected upstream of the particle filter. The temperature in the bed of the catalytic converter and/or at the inlet end of the oxidation catalytic converter is preferably sensed and compared with a stored respective reference value which correlates with the light-off temperature of the oxidation catalytic converter or corresponds to it. The unburnt components in the oxidation catalytic converter which are introduced into the exhaust gas when a late post-injection is activated and the heating operating setting is active, can therefore be converted. As a result, the application of heat into the exhaust gas rises so that even exhaust gas cleaning units which are arranged further away from the engine are quickly heated up.
In order to ensure that unburnt exhaust gas components in the oxidation catalytic converter are converted over the running time, that the stored reference value can be adapted, continuously or from time to time, in accordance with the aging state of the oxidation catalytic converter. If the reference value is exceeded, the late fuel post-injection is activated.
In a further refinement of the method, when either the heating operating setting or the basic operating setting is active, the fuel injection comprises at least one separate pre-injection. A separate pre-injection which is positioned in terms of timing before the main injection ensures stable combustion. This is advantageous both with respect to the late post-injection which is carried out in the heating operating setting and with respect to a low compression ratio.
Further stabilization of the combustion is achieved if, in a further refinement of the method, at least when the basic operating setting is active, double fuel pre-injection is performed.
In a further refinement of the method, when the heating operating setting is active, a fuel injection pressure which is reduced compared to the basic operating setting is set. This measure permits a further increased application of heat into the exhaust gas, thereby further increasing heating up speed of the exhaust gas post-treatment system, with simultaneously reduced NOx raw emissions.
In a further refinement of the method, when a third operating setting is active, an increased fuel injection pressure (compared to the basic operating setting) is set, so that an improved combustion in the combustion chambers can be achieved. The increase compared to the basic operating setting is typically between 50 bar and 500 bar. The rated injection pressure which is provided for the fuel injection system is therefore typically achieved under full load and at increased rotational speeds.
In a further refinement of the method, in the warmed-up state, a further, fourth operating setting is also performed, in which, when there is a changeover from the basic operating setting or from the third operating setting into the fourth operating setting, a late fuel post-injection is activated and/or the exhaust gas recirculation rate is reduced. The third operating setting is configured here to be optimized in terms of consumption, while the fourth operating setting facilitates heating the exhaust gas. Apart from the activated fuel post-injection or the reduced exhaust gas recirculation rate, the other internal combustion engine operating parameters of the basic operating setting preferably remain unchanged.
In a further refinement of the method, at least in one of the operating settings which is provided in the warmed-up state, an at least temporary inlet duct deactivation is provided. This measure is preferably carried out in a low load range (with less than approximately 50% of the rated load). However, at comparatively low rotational speeds the inlet duct deactivation can also be provided in the entire load range. The deactivated inlet duct is preferably what is referred to as a filling duct, while the non-deactivated inlet duct is preferably what is referred to as a swirl duct. Deactivating the filling duct achieves an increased swirl of the supply of gas and therefore better combustion, lower emission of particles and lower consumption of fuel. The deactivation of an inlet duct is preferably performed continuously as the load decreases.
In a further refinement of the method, at least in one of the operating settings which is provided in the warmed-up state, a glow plug which is assigned to a combustion chamber of the internal combustion engine is heated, at least temporarily. This measure is preferably also performed in a partial load range of the internal combustion engine and/or when the external temperature is low. As a result, the injected fuel is reliably ignited and therefore low raw emissions and low consumption of fuel are achieved. This is advantageous in particular in conjunction with a low compression ratio.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.